DEFORMATION-INDUCED CONFORMATIONAL-CHANGES IN STRETCHED SAMPLES OF AMORPHOUS POLY(ETHYLENE-TEREPHTHALATE)

The combination of Fourier transform Raman spectroscopy and thermal an alysis has been proved to be adequate for the study of the quantitativ e structural changes which take place in amorphous poly(ethylene terep hthalate) on stretching. The two-phase conformational model previously proposed for annealed samples was applied to uniaxially stretched sam ples. The samples were deformed at different temperatures and speeds. Different conformer contents were found in the stretched sample depend ing on the stretching conditions. In general, deformation induces a co nformational transition of gauche to trans. This behavior was lost at a narrow range of temperatures above the glass transition and at the l owest speeds, where the stretching seemed not to induce conformational changes. This different behavior has been associated to the high mobi lity of the polymer chains under these conditions, which imposes a dif ferent process of deformation marked by a high degree of chain slippin g. This kind of deformation is present all along the sample and with t he absence of necking in the uniaxial drawing process. (C) 1996 John W iley & Sons, Inc.